1) Field of the Invention
The present invention relates to a timing constraints creating device employed when designing a semiconductor integrated circuit.
2) Description of the Related Art
A bottom-up hierarchical designing is adopted when designing a semiconductor integrated circuit. Such designing involves dividing the whole circuit into a number of blocks, determining the area and the shape of each block, carrying out the detailed designing of each block based on a netlist, and building up the blocks from individual child blocks to form a parent block.
Timing constraints for each respective child block are created in the process of building the blocks by means of connecting the individual blocks. The timing constraints for the parent blocks are created by combining the timing constraints that are created for the child blocks. In this case, during data transfer between the child blocks, there are usually some datapaths that are excluded from a timing verification. Hence, before carrying out the timing optimization in the parent blocks, it is necessary to specify the datapaths that are to be excluded from the timing verification.
However, in the conventional technology, the designer manually specifies datapaths that are to be excluded from the timing verification during data transfer between two child blocks. There is always a possibility that the designer may miss out certain specifications. When such specifications miss occurs, the execution time increases as unnecessary datapaths are also optimized at the time of optimizing the timing for parent blocks. On the other hand, the datapaths that truly need to be optimized may not be optimized.
When a layout is created by using modified timing constraints, if a new error that has not been encountered before occurs, the designer again has to manually confirm whether the error has occurred in a datapath excluded from the timing verification or not. However, as the error occurs repeatedly, the user also has to confirm the same repeatedly, which is not at all desirable. Therefore, this aspect calls for an improvement.